To collimate with a conventional cylindrical detector of gamma rays, a long hollow tube is surrounded with shielding sufficient to attenuate un-collimated gamma rays. Much work has been done on improving collimators, but mostly for the lower energies used in medical applications (typically 0.511 MeV) and for exotic detectors. For high energy gamma rays (typically 2.6 MeV), such as those emitted from soil and objects in the soil, proper collimation requires an inordinate amount of shielding material on the order of hundreds of pounds of lead shielding.
Select embodiments of the present invention minimize the shielding material required for proper collimation of high energy gamma rays. In select embodiments of the present invention, the weight of shielding is minimized and the collimator tube is portable.